Speed-control and frequency-converter set



Nov. 27, 1928. 1,693,296

I J. l. HULL SPEED CONTROL AND FREQUENCY CONVERTER SET Filed Dec. 6. 1924 Invenbohz John I- Hull;

His Abnorne Patented Nov.27,192s. I 1,693,290 UNITED STATES PATENT OFFICE.

JOHN I. HULL, OF SCHENECTADY, NEW YORK, ASSIGNOR T GENERAL ELECTRIC COMPANY, A CORPORATION' 01 YORK;

1 SPEED-(XJNTBOL AND FREQUENCY-CONVERTER SET.

Application filed December 6, 1924. Serial .170. 754,405. U

My invention relates to speed control and osing a synchronous motor-generator set fr uency converter sets wherein an exciter etween the power line and the field cirmac ine having a commutator is connected cuit of the concatenated exciter. 1 in cascade with an induction machine for My invention will be better understood I the purpose of controlling its speed, and has from the following descri tion' when con- 00 for its object the provision of means for sidered in connection with t eaccompanying precluding self-excitation in sets of this drawing and its scope will be pointed. out character. in the appended claims.

It is well known that the s d of an in- The drawing shows an induction machine l0 duction machine concatenate with a suit- 1 arranged to have its stator winding conas able regulating machine may be varied in nected to a power line through a switch 3 and either direction through synchronism by to have its rotor winding connected through variation in the voltage of the regulating slip rings 4 and switch 5 either to a starting machine, and that the induction machine resistor 6 or to the commutator brushes 7 of '16 will function either as a enerator or as a a regulating machine 8. The concatenated 70 motor, when it is operated at speeds above machine 8 is shown as mechanically coupled or below synchronism. Such a control set o a driving machine 9, which has its staor machine aggregate is described in United or circuit interconnected with the line 2 States Letters Patent of Arthur Scherbius, hrough leads 10, and is arranged to have its No. 1,059,771, April 22, 1923, and in my completely separately excited field windings 75 United States Letters Patent N 0. 1,306,594, interconnected with the line 2 through a fre-- June 10, 1919, which relates to improvementsquency changer 11 coupled to the machine 1 on the arran ement set forth by the aforeand a synchronous motor-generator set comsaid Patent do. 1,059,771. The speed conpr sing machines 12 and 13. The machines 5 trol sets or machine aggregates shown by 12 and 13 may have the same number of a0 these patents are commonly known as poles and may be supplied with direct cur- S herbi s eed ontrol t nd will b so rent excitation through lines 14 and 15 redesignated ereinafter. spectively. The frequency changer 11 com- In the operation of a Scherbius speed conprises an armature winding connected at trol set, self excitation of the set can someone end to the slip rings 16 and at the other times occur for the reason that the same end to a commutator 17 which is arranged to power line or system is connected to the cooperate with brush pairs 18 and 19, 20 main induction machine and to the frequency and 21, and 22 and 23. The brushes of each I chan r through which the field current pair are connected to opposite ends of a dif- 35 of til; concatenated regulating machine ferent phase of the regu ating machine field m, is transmitted. Under these conditions wlnding and the corresponding brushes of changes in the electrical conditions of the the different pairs are arranged to be simulinduction machine produced by variation taneously moved about the commutator 17 in the regulating machine voltage are apt for the purpose of varying the field current to be reflected into the field circuit of'the and voltage of the, regu ating machine 8. 35 re lating machine, thus with suitable phase This movement ofthe brushes may be acre ations, tending to produce unstable opercomphshed by means of relatively movable ation or a cumulative effect and to superbrush yokes, one of which s arranged to impose .on the power line or system currents support and move the brushes 18, 20 and 22 of a frequency sometimes differing from that and the other of which is arranged to supm at which it is normally operated. This difiiport and move the brushes 19, 21 and 23, as culty is of course most likely to be encounset forth in United States reissue Letters tered when the generator capacity or the 09,- Patent of Hidee Klaas Schrage, No. 14,031, pacity of other a aratus connected to the D cember 14, 1915.

power line is sma lTas compared to that of The apparatus illustrated by the drawing, me

the Scherbius set and when the Scherbius in so far as it is described above, is adapted set is arranged in a well known manner to to control the speed of a load device coupled operate with a high or leading power factor. to the shaft of the induction machine 1. In the illustrated modification of my in- Since load devices of different kinds may be 5 vention, this difliculty is avoided by intercoupled to the shaft of the machine 1, my in invention is obviously not limited 'to the use of the speed control set just described in connection with any special form of load device. For the purpose of explaining my invention, I have shown it as utilized in a frequency converter set similar to that described and claimed in an application for United States Letters Patent of Carl M, Gilt, Serial No. 638,756, filed May 14, 1923, and assigned to the same assignee as the present application. This frequency converter set comprises a machine 2i coupled to the shaft of the induction machine 1 and arranged to be connected through a switch 25 with a power line or system which may be operated at a frequency different from that at which the power line 2 is operated. The machine 24 may be either of the synchronous or induction type. It is illustrated as a synchronous machine arranged to have its field current supplied through slip rings 27 and an adjustable resistor 28 from an exciter 29 which may be mounted on the same shaft as the machines 1, 11 and 24.

It is well known that the frequency of the usual alternating current system is apt to vary slightly from its normal value due to variations in the system load. When two such systems are interconnected through a frequency converter set of the type illus trated, power is transmitted through the converter set in one direction when the frequency of one of the systems is relatively high and through this set in the opposite direction when the frequency of the other set is relatively high. The amount of power transmitted through the converter set thus varies with the relation existing between the frequencies of the two-interconnected systems and, since these frequencies may vary over a range sufliciently large to overload the converter set, it is desirable to provide means for limiting the converter load to a safe value. This result may be accomplished through adjustment of the brush pairs 18-19, 2021 and 22-23 in a manner to vary the field current of the regulating machine 8. As shown in the drawing, the pairs of brushes are in each case located so that the two brushes of each pair coincide in position on one commutator bar. Under these conditions, no current is supplied from the frequency changer to the field winding of the regulating machine 8. The brush arrangement is such that the brushes 18, 20

and 22 may be simultaneously moved in one direction by any suitable means while the brushes 19, 21 and 23 are likewise moved in the opposite direction and vice versa. When the brushes 18, 20 and 22 are moved in one direction from their illustrated position, therefore, the voltage of the regulating machine 8 is increased in one direction and when this group of brushes is moved in the opposite direction from this .position, the

motor 1 operates on the existing frequency of line 2 and with the desired motor or generator load at exactly the speed de-f manded by machine 24. g

As previously indicated, my invention relates particularly to meansfor avoiding self excitation of the machine aggregate and differs from that set forth in the aforesaid Gilt application in that the frequency changer exciter is connected to the power line through self-excitation avoiding means, illustrated as a synchronous motor-generator feet, in stead of through a transformer. With this arrangement, the excitation of the concatenated regulating machine is determined by the line frequency and the brush setting, and variation in the voltage or current of the power lineproduced by changes in the operation of the induction machine or the con-' verter set are rendered incapable of affecting the excitation of the concatenated exciter machine in a manner to produce self-excitation of the set. The synchronous motor-generator set thus forms a tie between the power line and the frequency changer exciter 'by means of which current of the proper fre-1 quency is transmitted through the field winding of the concatenated regulating machine without danger of producing self-excitation of the complete set.

,I have ex lained my invention b illustrating and escribing a certain specific embodiment thereof, but it will be readily un-' derstood by those skilled in the art that the arran ement of this embodiment may be modi ed in certain of its details. I, accordingly, do not wish to be restricted tothe particular arrangement disclosed herein by way of example for the purposeof setting forth my invention in accordance with the patent statutes. The terms of the a pended claims are, therefore, not restricte to the precise arrangement disclosed, but are intended to cover all changes and modifications '.within the true spirit and scope of my vention.

What I claim as new and desire to secure by Letters Patent of the United States, is: 1. In combination, a, ower line, an induction machine connecte to said'power line, a regulating machine concatenated with said induction machine, a completely separately machine, a completely separately excited field winding on said regulating machine, and means for supplying excitation energy from said power line to said field winding comprising a frequency changer and a synchronous motor generator set, said means being arranged to be responsive to the frequency changes of said line, but nonrespon- 20 sive to the voltage changes thereof In witness whereof, I have hereunto set my hand this 5th day of December, 1924.

JOHN I. HULL. 

